The invention relates to improved microcomputer architectures, particularly for use in battery powered equipment.
While microprocessors are general-purpose data processing devices, many microprocessor applications are specific in nature. When the application for a microprocessor is not principally the provision of computer facilities, but the inclusion of a microprocessor in the equipment is merely incidental, being for example simply a convenient technical solution to an internal control problem, then the application is termed an "embedded microprocessor" application. Since the provision of computing facilities in embedded applications is not the principal aim, the embedded microprocessor should ideally impact as little as possible on the size, cost and power consumption while satisfying the main objectives of the application.
A typical embedded microprocessor application is a radiotelephone such as a cellular telephone. A cellular telephone is operable in conjunction with a cellular telephone system of remotely located base stations and switches to provide two-way voice and data communications for a user of the cellular telephone. The principal objective of the microprocessor application is to provide two-way voice communication between the cellular subscriber and a remote base station or another telephone subscriber. An incidental need arises for a microcomputer to handle aspects such as receiving and responding to signalling messages from the network that address calls to particular phones or carry other commands during a call. Examples of such commands include turning the mobile phone transmit power up and down or causing the phone to change frequency to handover to different base stations as the telephone moves from one area to another.
An important design goal for radiotelephones such as a cellular telephone is the minimization of current drain by the electrical components of the radiotelephone. Current drain is related to battery life. It is desirable to maximize battery life for user convenience and for other reasons. To maximized battery life, it is desirable to minimize current drain during all operating modes of the radiotelephone.
Modern cellular phones have increasing requirements for software control programs to handle ever more sophisticated network features such as digital voice transmission, data modes, short message services, etc. The volume of software typically included in a phone today is stretching the capabilities of the simplest low-power microprocessors that typically are limited to 64k bytes of memory address space. Unfortunately, processors designed to address much greater memories were conceived for applications other than the battery-power-limited embedded application such as a radiotelephone. Such a processor would severely impact battery life if used in a battery powered application. Power consumption of a microprocessor during execution is also related to the number of memory bits that have to be read or written to perform a given task. Thus in the interests of low power consumption for embedded, battery-powered applications, a high program efficiency is desirable. Consequently, there is a need for a new microcomputer architecture that is convenient to program, has much expanded address space, and yet is efficient on program memory utilization and power consumption for embedded applications.